As circular waveguides have met with increasing usage in UHF transmission towers, a number of problems have surfaced. A typical transmission tower may vary in height from a few hundred to more than 1500 feet. A vertical run of circular waveguide corresponding to the tower height must be erected and supported in the tower. Since the tower is made of steel and the waveguide is made of aluminum of copper, the waveguide tends to creep axially relative to the tower due to differential expansion accompanying changes in temperature. The waveguide is further subject to severe lateral forces due to wind loading, tending to deform it at the points of support. The likelihood of deformation is increased because the waveguide has a sidewall of relatively soft metal which is extremely thin in relation to its diameter. Such deformation tends to introduce discontinuities into the energy mode transmitted through the waveguide, resulting in ghosting and other abnormalities.
Attempts have been made heretofore to suspend waveguides from transmission towers by means of coil extension springs to compensate for the differential expansion rates between the tower and the waveguide. Such systems have a number of disadvantages. Among these are large hanger size requiring a large distance from the waveguide center line to the hanger mounting surface on the tower, with resulting lack of rigidity; excessive clearance area required in order to accommodate the spring mechanism; attachment to the waveguide only at a flange connection, thereby requiring additional hanger members; critically of aligning during installation to avoid binding of the hanger mechanism; excessive waveguide and hanger wear because of metal to metal contact; possibility of damage to the waveguide from wind load forces; and excessive costs.
Another prior suspension makes use of conventional extension spring type hangers to support the waveguide. This type of suspension also has disadvantages such as variation of spring force with the amount of spring deflection; requirement for excessive length in the spring in its working area; necessity for precluding loss of parts from the transmission tower in event of spring failure; and likelihood of damage to the waveguide from wind load in event of spring failure.